1. Field of the Invention
The present invention relates to an idling speed controller and an idling speed control method for an internal-combustion engine for controlling the revolutional speed of the internal-combustion engine.
2. Description of the Related Art
When the revolutional speed of an internal-combustion engine becomes lower due to a load applied to the internal-combustion engine, the revolution of the internal-combustion engine becomes unstable. This generates vibration which is uncomfortable for the driver is and tends to cause engine stall at the start of driving an idling speed controller is conventionally known where the revolutional speed of en internal-combustion engine is controlled in accordance with the state of the load applied to the internal-combustion engine when the internal-combustion engine is in an idling state. Such an idling speed controller compares the actual revolutional speed of the internal-combustion engine with a predetermined target revolutional speed, determines a control amount so as to match the actual revolutional speed with the target revolutional speed, and drives an actuator so that an air amount corresponding to a control amount can be supplied to the internal-combustion engine. This feedback control of the revolutional speed of the internal-combustion engine is a basis for the idling speed control.
Japanese Laid-Open Patent Publication No. 60-19936 discloses an idling speed control method for an internal-combustion engine. According to this method, when the decrease in the revolutional speed of the internal-combustion engine reaches or exceeds a predetermined value, the air amount supplied to the internal-combustion engine is increased by opening an idling speed control (ISC) valve.
According to the above disclosed idling speed control method, the ISC valve is opened even when the revolutional speed of the internal-combustion engine decreases below the predetermined value. When noise enters an electronic control unit (ECU) due to a disturbance (e.g., external radio wave), the air amount (intake amount) supplied to the internal-combustion engine may unnecessarily increase. This results in an unnecessary increase in the revolutional speed of the internal-combustion engine.
An objective of the present invention is to provide an idling speed controller and an idling speed control method for an internal-combustion engine, where the revolutional speed of the internal-combustion engine is not increased when due to noise, a decrease in the revolutional speed of the internal-combustion engine reaches or exceeds a predetermined values.